Liquid bath reference cavity

ABSTRACT

An improved liquid-bath-type reference cavity is provided, in which the cavity is formed by a closed-end metallic bellows. The walls of the bellows are fabricated from good thermal conducting materials with very thin wall thickness, which increases the effective surface area in contact with the liquid and provides a rapid stabilization of the cavity to the temperature of the liquid bath in which it is immersed.

United States Patent [72] Inventor Robert T. Ensor Redding, Conn. 211Appl. No. 884,098 [22] Filed Dec. 11, 1969 [45] Patented Jan. 4, 1972[73] Assignee Barnes Engineering Company Stamford, Conn.

[54] LIQUID BATH REFERENCE CAVITY 2 Claims, 1 Drawing Fig.

{52] US. Cl 73/1 F, 250/84 [51] Int. Cl G0lj 5/00 [50] Field of Search.73/l F, 355; 250/84, 85

[56] References Cited UNITED STATES PATENTS 3,348,408 10/1967 Engborg73/1 F 3,419,709 12/1968 DeBell OTHER REFERENCES Kostkowski, H. J. etal. in Temperature lts Measurement and Control in Science & lndustryVol. 111 Herzfeld ed. Part 1. Basic Concepts, Standards and Methods,Brickwedde, ed. Reinhold Pub. Co. NY. 1962 paper No. 47 pages 460 & 461relied upon QC271AG Primary Examiner-S. Clement Swisher AttorneysJosephLevinson and Robert Ames Norton ABSTRACT: An improved liquid-bath-typereference cavity is provided, in which the cavity is formed by aclosed-end metallic bellows. The walls of the bellows are fabricatedfrom good thermal conducting materials with very thin wall thickness,which increases the effective surface area in contact with the liquidand provides a rapid stabilization of the cavity to the temperature ofthe liquid bath in which it is immersed.

PATENTEU JAN 41972 III INVENTOR. 7"i ENSOP A T TOR/VF Y ROBERT BY fLIQUID BATI-I REFERENCE CAVITY BACKGROUND OF THE INVENTION Liquid bathtype reference cavities provide an insulated reservoir which is filledwith a liquid. A plastic cavity having, generally, a test-tube shape, isimmersed along with a laboratory type thermometer in the liquid bath,and in theory the test-tube cavity stabilizes at the temperature of theliquid bath. Radiometers and other types of instrumentation can becalibrated by pointing them into the cavity so their entire fields ofview are observing nothing but the interior of the testtube cavity. Theinstruments readout can be set to match the temperature indicated by thethermometer. One of the major difficulties encountered is that thecavity, which is made of plastic, has poor conductive properties andthus does not readily stabilize to the temperature of the liquid bath.Accordingly, the actual emitted temperature of the cavity may be severaldegrees different from that of the liquid bath, causing an error in thereadouts of the instrument calibrated to the reference. Furthermore,outside radiation which is reflected into the cavity has also causederror.

Accordingly, it is an object of this invention to provide an improvedliquid-bath-type reference cavity which minimizes calibration errors.

SUMMARY OF THE INVENTION The improved liquid-bath-type reference cavityof this invention is obtained by using a closed-end thermally conductivebellows whose convolutions increase the effective surface area incontact with the liquid bath and in addition scatter and thus minimizethe effects of unknown outside radiation being reflected into theaperture of instruments being calibrated.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a side view, partly insection, of the liquid bath type reference cavity embodied in thisinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, theliquid bath reference cavity has a body portion having a reservoir 12mounted therein and separated from the body 10 by insulation 14. Theopen end of the body portion 10 of the reference cavity is covered by aclosing plate 16 having a central opening 18 therein. The reservoir 12is filled with a suitable liquid 15, such as cooled or heated water.Mounted in the central opening 18 of the closing plate 16 is a thermallyconductive bellows 20. Bellows 20 has a closed end 22 and an open end 24such that the bellows 20 as mounted provides an enclosed cavity. Thebellows 20 is fabricated from good thennal conductive material such asphosphor, bronze, or copper with a very thin wall thickness, on theorder of 0.005 inch to 0.01 inchjA standard laboratory type mercurythermometer 26 or any other suitable temperature indicating means isimmersed in the liquid bath 15 through a grommet 28 mounted in theclosing plate 16.

In operation, instruments to be calibrated are pointed into the open end24 of the bellows 20 which forms a cavity therein so that the entirefield of view of the instrument is observing nothing but the interior ofthe cavity of the bellows 20. The readout of the instruments to becalibrated are set to match the temperature indicated by the thermometer26. The advantages of the present invention reside in the use of thebellows 20 as the cavity. The convolutions of the bellows 20 increasethe effective surface area in contact with the liquid 15, and since thebellows 20 is constructed of good thermally conductive materials, thecavity quickly stabilizes at the temperature of the liquid bath which isread on the thermometer 28. In addition, the convolutions of the bellows20 help to scatter, and thus minimize, the effects of unknown outsideradiation being reflected into the aperture of the instruments beingcalibrated. The interior surface of the bellows 20 is also blackened toreduce reflectivity and improve the emissivity of the caviotgiogeningliByutilizing the improved construction that IS emb e in s invention,tests on the bellows cavity showed that the measured temperature of thereference liquid and the emitted cavity temperature are the same withinA C. or better.

I claim:

1. A liquid-bath-type reference cavity comprising in combination a. aninsulated reservoir having an opening on one end thereof,

b. said reservoir being filled with a liquid,

c. a closed-end thennally conductive bellows submerged in said liquidand having its open end mounted in the opening of said reservoir,thereby providing a reference cavity the temperature of which is that ofthe liquid,

d. means submerged in said liquid for indicating the temperature of saidliquid.

2. The reference cavity set forth in claim I wherein said thermallyconductive bellows is metallic having a wall thickness on the order of0.005 to 0.010 inches with its interior surface blackened.

1. A liquid-bath-type reference cavity comprising in combination a. aninsulated reservoir having an opening on one end thereof, b. saidreservoir being filled with a liquid, c. a closed-end thermallyconductive bellows submerged in said liquid and having its open endmounted in the opening of said reservoir, thereby providing a referencecavity the temperature of which is that of the liquid, d. meanssubmerged in said liquid for indicating the temperature of said liquid.2. The reference cavity set forth in claim 1 wherein said thermallyconductive bellows is metallic having a wall thickness on the order of0.005 to 0.010 inches with its interior surface blackened.